Semiconductor device with reduced via resistance

ABSTRACT

A method of fabricating a semiconductor interconnect structure by providing a semiconductor structure with a dielectric layer with and an embedded electrically conductive structure. A dielectric capping layer and a metal capping layer separating a second dielectric layer located above the first dielectric layer. The segment of metal capping layer covers at least a portion of a top surface of the first electrically conductive structure. Exposing parts of both the first electrically conductive structure and the dielectric capping layer by forming an opening in the second dielectric layer and the metal capping layer. Forming a second electrically conductive structure in the opening, such that (i) the second electrically conductive structure is located over part of the dielectric capping layer, and (ii) the second electrically conductive structure is in electrical contact with the first electrically conductive structure.

BACKGROUND OF THE INVENTION

The present invention relates generally to semiconductor devices, andmore particularly to copper interconnects and methods of theirfabrication.

Manufacture of a semiconductor device is normally divided into two majorphases. The “front end of the line” (FEOL) is dedicated to the creationof all the transistors in the body of the semiconductor device, and the“back end of the line” (BEOL) creates the metal interconnect structures,which connect the transistors to each other as well as provide power tothe devices. The FEOL consists of a repeated sequence of steps thatmodifies the electrical properties of part of a wafer surface and growsnew material above selected regions. Once all active components arecreated, the second phase of manufacturing (BEOL) begins. During theBEOL, metal interconnects are created to establish the connectionpattern of the semiconductor device.

Semiconductor devices generally include a plurality of circuits whichform an integrated circuit fabricated on a semiconductor substrate. Toimprove the performance of the circuits, low k dielectric materials,having a dielectric constant of less than silicon dioxide, are usedbetween circuits as inter-layer dielectric (ILD) to reduce capacitance.Interconnect structures made of metal lines or metal vias are usuallyformed in and around the ILD material to connect elements of thecircuits. Within a typical interconnect structure, metal lines runparallel to the semiconductor substrate, while metal vias runperpendicular to the semiconductor substrate. An interconnect structuremay consist of multilevel or multilayered schemes, such as, single ordual damascene wiring structures.

There are many failure mechanisms that affect the reliability of anintegrated circuit. Time Dependent Dielectric Breakdown (TDDB) is afailure mechanism where the dielectric material of the ILD breaks downas a result of long-time application of electrical stresses, such ashigh current density. The breakdown leads to formation of a conductingpath through the dielectric material and between metal interconnects viasurface diffusion of the metal interconnect structures, i.e., wires andvias. In time, the conducting path will form a short betweeninterconnect structures causing a failure.

SUMMARY

An embodiment of the present invention discloses a method of fabricationof a semiconductor interconnect structure. The method includesfabricating a semiconductor interconnect structure by providing asemiconductor structure including a dielectric layer with andelectrically conductive structure embedded therein. A second dielectriclayer is located above the first dielectric layer. The second dielectriclayer and the first dielectric layer have a segment of a dielectriccapping layer and a segment of a metal capping layer locatedtherebetween. The segment of metal capping layer covers at least aportion of a top surface of the first electrically conductive structure.The method includes forming an opening in the second dielectric layerand the metal capping layer, thereby exposing at least a portion of thefirst electrically conductive structure and a portion of the dielectriccapping layer. The method includes forming a second electricallyconductive structure in the opening, such that a first bottom portion ofthe second electrically conductive structure is located over a portionof the dielectric capping layer, and such that a second bottom portionof the second electrically conductive structure is in electrical contactwith the portion of the first electrically conductive structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of a semiconductor devicecontaining a back-end-of-line (BEOL) metal interconnect, in accordancewith an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a semiconductor device upon whichthe interconnect structure of FIG. 1 is be fabricated, in accordancewith an embodiment of the present invention.

FIG. 3A depicts fabrication steps, in accordance with an embodiment ofthe present invention.

FIG. 3B depicts additional fabrication steps, in accordance with anembodiment of the present invention.

FIG. 3C depicts additional fabrication steps, in accordance with anembodiment of the present invention.

FIG. 4A depicts additional fabrication steps, in accordance with anembodiment of the present invention.

FIG. 4B depicts additional fabrication steps, in accordance with anembodiment of the present invention.

FIG. 4C depicts additional fabrication steps, in accordance with anembodiment of the present invention.

FIG. 5 depicts additional fabrication steps, in accordance with anembodiment of the present invention.

FIG. 6 depicts additional fabrication steps, in accordance with anembodiment of the present invention.

FIG. 7 illustrates a cross-sectional view of a semiconductor devicecontaining a back-end-of-line (BEOL) metal interconnect with a secondliner, in accordance with an embodiment of the present invention.

FIG. 8 depicts additional fabrication steps, in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION

Embodiments, in accordance with the present invention, recognize thatmetal via resistance increases with technology as the size of componentfeatures shrink. The combination of materials, and electrical propertiesof the materials used in fabrication of “back end of the line” (BEOL)metal interconnects creates vias with higher resistance as the size ofthe structural elements decrease. Metal via resistance is a combinationof the resistance associated with the bulk metal, the sidewall metal,and the liner material within the metal via. Embodiments recognize thatthe portion of via resistance from the high resistivity liner materialdominates the portion of via resistance from either the bulk metal, orthe sidewall metal within the metal via. Embodiments provide afabrication process for a metal interconnect which selectively removesthe liner material at the bottom of a metal via. Removal of the highresistivity liner material at the bottom of the metal via reduces theresistance of the electrical connection between the metal via and ametal wiring landing pad.

An alternate embodiment provides a fabrication process for a metalinterconnect which selectively removes the liner material at the bottomof a metal via, and replaces or adds to the original liner material witha second liner material with lower resistivity. In some embodiments, thesecond liner material includes conductive materials with low resistivitywhich provide for wettability at the bottom of the metal via duringplating to prevent defects from voiding at the bottom.

Embodiments recognize that misalignment of the metal via to the metalwiring landing pad is a byproduct of registration tolerances inpatterning during the fabrication process, and the opportunity for suchmisalignment will increase with technology as the size of componentfeatures shrink. In some embodiments, in the case of a partially landedmetal via, the via is not be completely surrounded by a diffusionbarrier material due to non-selectivity of a dielectric capping layerformed directly above the metal wiring landing pad. In some scenarios,without a selective diffusion barrier, ions of the bulk metal diffuseover time into the inter-layer dielectric (ILD) layer causing anelectrical short due to Time Dependent Dielectric Breakdown (TDDB).Embodiments, in accordance with the present invention, provide adiffusion barrier or capping layer comprised of a dielectric component,and a metal component.

Embodiments define an interconnect structure with a bottom conductivelayer, an insulating dielectric layer, a metal capping layer, and ametal conductive via, where the conductive via and bottom conductivelayer are electrically connected. Fabrication methods are disclosed foretching the metal liner material from the bottom of the metal via.Reduced TDDB defects combined with reduced resistance of interconnectsoffer the potential to deliver superior performance and reliability forsemiconductor applications in electronic devices.

Embodiments generally provide a metal interconnect between a metal wireand a metal via with reduced resistance surrounded by a diffusionbarrier permitting reproducible and manufacturable designs. Detaileddescription of embodiments of the claimed structures and methods aredisclosed herein; however, it is to be understood that the disclosedembodiments are merely illustrative of the claimed structures andmethods that may be embodied in various forms. In addition, each of theexamples given in connection with the various embodiments is intended tobe illustrative, and not restrictive. Further, the Figures are notnecessarily to scale, some features may be exaggerated to show detailsof particular components. Therefore, specific structural and functionaldetails disclosed herein are not to be interpreted as limiting, butmerely as a representative basis for teaching one skilled in the art tovariously employ the methods and structures of the present disclosure.

References in the specification to “one embodiment”, “an embodiment”,“an example embodiment”, etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

For purposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, andderivatives thereof shall relate to the disclosed structures andmethods, as oriented in the drawing Figures. The terms “on”, “over”,“overlying”, “atop”, “positioned on”, or “positioned atop” mean that afirst element, such as a first structure, is present on a secondelement, such as a second structure, wherein intervening elements, suchas an interface structure may be present between the first element andthe second element. The terms “direct contact”, “directly on”, or“directly over” mean that a first element, such as a first structure,and a second element, such as a second structure, are connected withoutany intermediary conducting, insulating or semiconductor layers at theinterface of the two elements. The terms “connected” or “coupled” meanthat one element is directly connected or coupled to another element, orintervening elements may be present. The terms “directly connected” or“directly coupled” mean that one element is connected or coupled toanother element without any intermediary elements present.

Referring now to the Figures, FIG. 1 illustrates a cross-sectional viewof a semiconductor device containing a back-end-of-line (BEOL) metalinterconnect, i.e. interconnect structure 100, in accordance with anembodiment of the present invention. Interconnect structure 100 includeslower interconnect level 202 and upper interconnect level 210 which areseparated, in part, by a capping layer comprised of metal capping layer312 and dielectric capping layer 314. In this embodiment, lowerinterconnect level 202 is located above a semiconductor substrate (notshown) including one or more semiconductor front-end-of-line (FEOL)devices. Lower interconnect level 202 includes dielectric layer 204, andan embedded conductor comprised of liner material 206, and conductivematerial 208. Liner material 206 acts as a diffusion barrier separatingconductive material 208 from dielectric layer 204. As such, together,liner material 206 and conductive material 208 constitute anelectrically conductive structure embedded in dielectric layer 204.Upper interconnect level 210 includes a second dielectric layer, i.e.,dielectric layer 416, which has two via openings located therein for via110, and via 120. The two via openings for vias 110 and 120, each exposea portion of conductive material 208 in lower interconnect level 202.The two via openings for vias 110 and 120 are filled with liner material418 and conductive material 622, which forms an electrical connectionbetween lower interconnect level 202 and upper interconnect level 210.As such, vias 110 and 120 are seen as a type of electrically conductivestructures. Liner material 418 acts as a diffusion barrier separatingconductive material 622 from dielectric layer 416. Although thestructure shown in FIG. 1 illustrates an interconnect having two vias,other embodiments include any number of such vias in dielectric layer416. In some embodiments, one or more such vias expose other conductiveregions embedded in dielectric layer 204.

In accordance with an embodiment of the present invention, interconnectstructure 100 includes a partially landed via, via 110, above conductivematerial 208. Via 110 is partially landed on conductive material 208such that only a portion of the bottom via surface is directly onconductive material 208. A second portion of the bottom via surface ofvia 110 is directly on dielectric capping layer 314. A first portion ofthe sidewall of via 110 is connected to dielectric capping layer 314,and a second portion of the sidewall of via 110 is connected to metalcapping layer 312. In some embodiments, the sidewall of via 110 includeliner material 418. Both metal capping layer 312 and dielectric cappinglayer 314 act as a diffusion barrier separating conductive materials 208and 622 from dielectric layers 204 and 416. In other words, both metalcapping layer 312 and dielectric capping layer 314 inhibit the migrationof metals or other elements from conductive materials 208 and 622 todielectric layers 204 and 416.

In accordance with an embodiment of the present invention, both vias 110and 120 are constructed with portions of metal liner material 418selectively removed from the bottom of each via. In some embodiments,portions of conductive material 208 directly under the removed portionsof metal liner material 418 are selectively removed. In someembodiments, removal of a portion of conductive material 208 ensuresthat metal liner material 418 is completely removed. In someembodiments, removal of a portion of conductive material 208 results ina texturing of the bottom via surface to aid adhesion of conductivematerial 622. Conductive material 622 fills in vias 110 and 120, anddirectly contacts conductive material 208 to reduce or minimize viaresistance. Removal of portions of metal liner material 418 provides areduction in overall via resistance.

In some embodiments, above upper interconnect level 210 includes upperwiring layers (not shown), or escape wiring leading to the surface aboveinterconnect structure 100. In some embodiments, such above the upperwiring layers, are protective layers (not shown), such as oxides,nitrides, and polyimide films, as are standard in semiconductormanufacture.

FIGS. 2-6 depict an embodiment for fabricating interconnect structure100 with vias 110 and 120. FIG. 2 is a cross-sectional view of asemiconductor device upon which the interconnect structure of FIG. 1 isfabricated, in accordance with an embodiment of the present invention.In some embodiments, lower interconnect level 202 is located above asemiconductor substrate (not shown) including one or more semiconductorfront-end-of-line (FEOL) devices. In some embodiments, the semiconductorsubstrate includes an electrically semiconducting material, aninsulating material, a conductive material, devices, or structures madeof these materials or any combination thereof (e.g., a lower level of aninterconnect structure). In certain embodiments, the semiconductorsubstrate is comprised of a semiconducting material, such as Si, SiGe,SiGeC, SiC, Ge alloys, GaAs, InAs, InP, and other compoundsemiconductors, or organic semiconductors. In some embodiments, inaddition to the above listed semiconducting materials, thesemiconducting material includes a layered semiconductor, such as, forexample, Si/SiGe, Si/SiC, SOIs, or silicon germanium-on-insulators(SGOIs). In some embodiments, these semiconductor materials form adevice, devices, or structures, which are either discrete orinterconnected, or a combination thereof.

In certain embodiments, the semiconductor substrate includes one or moresemiconductor devices, such as complementary metal oxide semiconductor(CMOS) devices or other field effect transistors (FETs), strainedsilicon devices, carbon-based (carbon nanotubes and/or graphene)devices, phase-change memory devices, magnetic memory devices, magneticspin switching devices, single electron transistors, quantum devices,molecule-based switches, and other switching or memory devices that canbe part of an integrated circuit formed therein. In other embodiments,the semiconductor substrate includes an electrical insulating material,such as an organic insulator, an inorganic insulator, or a combinationthereof. In some embodiments, the semiconductor substrate includeselectrically conducting material, for example, polysilicon, an elementalmetal, an alloy including at least one elemental metal, a metalsilicide, a metal nitride, etc., or combinations thereof includingmultilayers.

In the illustrative example of FIG. 2, lower interconnect level 202includes dielectric layer 204, and a conductor embedded thereincomprised of liner material 206, and conductive material 208. In someembodiments, dielectric layer 204 of lower interconnect level 202 is anyILD layer including inorganic dielectrics or organic dielectrics, and iseither porous or non-porous, or a combination thereof. Examples ofsuitable dielectrics include, but are not limited to, SiC, Si₃N₄, SiO₂,a carbon doped oxide, SiC(N,H), a low-K dielectric, or multilayersthereof. In some embodiments, dielectric layer 204 is formed over thesurface of the semiconductor substrate using an appropriate depositiontechnique including, but not limited to, physical vapor deposition(PVD), plasma assisted chemical vapor deposition (PACVD), chemical vapordeposition (CVD), plasma enhanced chemical vapor deposition (PECVD), lowpressure chemical vapor deposition (LPCVD), atomic layer deposition(ALD), chemical solution deposition (such as spin coating), orevaporation. In some embodiments, the thickness of dielectric layer 204varies depending on the dielectric material used and the number ofdielectric layers within lower interconnect level 202. For typicalinterconnect structures, dielectric layer 204 has a thickness from about100 nm to 450 nm.

In some embodiments, conductive material 208 of lower interconnect level202 forms a conductive region or feature embedded in dielectric layer204. In some embodiments, the conductive region or feature is formed byconventional damascene patterning or subtractive etch patterningutilizing lithographic, etching, and deposition processes. For example,a photoresist layer is applied to the surface of dielectric layer 204.The photoresist layer is exposed to a desired pattern of radiation, anddeveloped utilizing a conventional resist developer. The patternedphotoresist layer is used as an etch mask to transfer the pattern intodielectric layer 204. The etched region of dielectric layer 204 is thenfilled with conductive material 208 to form the conductive region orfeature. Conductive material 208 includes, but is not limited to,polysilicon, a conductive metal, an alloy of two or more conductivemetals, a conductive metal silicide, or any combination of two or moreof the foregoing materials. In some embodiments, conductive material 208is comprised of one or more of Cu, Al, W, Ti, TiN, Cu alloy (such asAlCu), or any other useful conductive material or alloy(s). Conductivematerial 208 is deposited into the etched region of dielectric layer 204using an appropriate deposition technique including, but not limited to,sputter deposition, ALD, CVD, PVD, PECVD, electrochemical deposition(ED), electroplating, or other deposition techniques. In someembodiments, after deposition, a conventional planarization process,such as chemical mechanical polishing (CMP), is used to provide astructure in which conductive material 208 has an upper surface that issubstantially coplanar with the upper surface of dielectric layer 204.

Embodiments provide for separation of conductive material 208 fromdielectric layer 204 by a diffusion barrier layer, such as linermaterial 206. In some embodiments, liner material 206 includes, but isnot limited to, one or more of: Ta, TaN, Ti, TiN, Ru, RuTaN, RuTa, W,WN, or any other material that serves as a barrier to prevent aconductive material from diffusing into a dielectric material layer. Insome embodiments, liner material 206 is formed by a deposition processincluding, but not limited to, ALD, CVD, PVD, PECVD, ED, sputtering, orplating. In some embodiments, liner material 206 also includes a bilayeror multi-layer structure that includes a lower layer of a metallicnitride, such as TaN, and an upper metallic layer, such as Ta. In someembodiments, the thickness of liner material 206 varies depending on theexact means of the deposition process and the material employed.Typically, liner material 206 has a thickness from about 4 nm to about40 nm, with a thickness from about 7 nm to about 20 nm being moretypical.

FIG. 3A depicts fabrication steps, in accordance with an embodiment ofthe present invention. After forming the at least one conductive featurecomprising conductive material 208 within dielectric layer 204, acapping layer is selectively formed on the surface of conductivematerial 208 of lower interconnect level 202. Metal capping layer 312 isformed by a conventional deposition process including, but not limitedto, CVD, ALD, or electroless plating. The various deposition conditionsare optimized to provide selective deposition to the conductive surfaceof conductive material 208 without utilizing a mask. In someembodiments, metal capping layer 312 is any suitable metallic cappingmaterial including, but not limited to, Co, Ru, W, Ta, Ti, P, Rh, andany alloy or combination thereof. Metal capping layer 312 provides adiffusion barrier between conductive material 208 of lower interconnectlevel 202 and dielectric layer 416 of upper interconnect level 210, asshown in FIG. 1.

FIG. 3B depicts additional fabrication steps, in accordance with anembodiment of the present invention. After forming metal capping layer312, a second capping material, dielectric capping layer 314 is blanketdeposited over the surface of both dielectric layer 204 and metalcapping layer 312. In some embodiments, dielectric capping layer 314 isdeposited on dielectric layer 204 and metal capping layer 312 using anappropriate deposition technique (discussed above). In some embodiments,dielectric capping layer 314 is any suitable dielectric capping materialincluding, but not limited to, SiC, Si₄NH₃, SiO₂, or multilayersthereof. Dielectric capping layer 314 provides a diffusion barrierbetween conductive material 622 of upper interconnect level 210, asdepicted and described in FIG. 1, and dielectric layer 204 of lowerinterconnect level 202. Embodiments provide that dielectric cappinglayer 314 has a dielectric constant higher than dielectric layer 204 oflower interconnect level 202, and dielectric layer 416 of upperinterconnect level 210, as depicted and described in FIG. 1.

FIG. 3C depicts additional fabrication steps, in accordance with anembodiment of the present invention. In some embodiments, afterdeposition, a conventional planarization process, such as CMP, is usedto provide a structure in which both metal capping layer 312 anddielectric capping layer 314 have an upper surface that is substantiallycoplanar with the upper surface of lower interconnect level 202. AfterCMP, metal capping layer 312 and dielectric capping layer 314 have athickness from about 15 nm to about 55 nm, with a thickness from about25 nm to about 45 nm being more typical. In some embodiments, thethickness of the capping layer materials varies depending on the exactmeans of the deposition process as well as the materials employed.

FIG. 4A depicts additional fabrication steps, in accordance with anembodiment of the present invention. Next, upper interconnect level 210is formed by depositing dielectric layer 416 on the upper exposedsurfaces of metal capping layer 312 and dielectric capping layer 314. Insome embodiments, dielectric layer 416 is the same or differentdielectric material as that of dielectric layer 204 of lowerinterconnect level 202. In some embodiments, dielectric layer 416 iscomprise dielectric material including, but not limited to: SiC, Si₃N₄,SiO₂, a carbon doped oxide, SiC(N,H), a low-K dielectric, or multilayersthereof. In various embodiments, dielectric layer 416 is Si₃N₄ with atypical thickness of about 100 nm to 450 nm. A person of ordinary skillin the art will recognize that CMP steps may be inserted after thedielectric deposition process to planarize the surface of dielectriclayer 416. In some embodiments, CMP utilizes a combination of chemicaletching and mechanical polishing to smooth the surface and even out anyirregular topography.

Using a conventional lithography process, an etch mask (not shown) isdeposited over dielectric layer 416, and then patterned to createopenings in the etch mask. The openings define at least two portions ofdielectric layer 416 to be removed, which form openings for vias 110 and120 of upper interconnect level 210, in accordance with an embodiment ofthe present invention. FIG. 4A illustrates vias 110 and 120 with anoutline surrounding the via openings in dielectric layer 416. Dielectriclayer 416 is etched down to metal capping layer 312 and dielectriccapping layer 314 forming vias 110 and 120 therein. A portion of the topsurface of metal capping layer 312 and a portion of the top surface ofdielectric capping layer 314 are exposed at the bottom of via 110. Asecond portion of the top surface of metal capping layer 312 is exposedat the bottom of via 120. In some embodiments, the etching used intransferring the via pattern comprises a dry etching process, a wetchemical etching process or a combination thereof. The term “dryetching” is used herein to denote an etching technique such asreactive-ion etching (RIE), ion beam etching, plasma etching, or laserablation. In the illustrative embodiment, vias 110 and 120 are formed byemploying an RIE process. RIE uses chemically reactive plasma, generatedby an electromagnetic field, to remove various materials. A person ofordinary skill in the art will recognize that the type of plasma usedwill depend on the material being removed. In some embodiments, thepatterned etch mask is not removed at this point. In other embodiments,the patterned etch mask is removed at this point.

FIG. 4B depicts additional fabrication steps, in accordance with anembodiment of the present invention. Using a conventional etchingprocess, one or more portions of metal capping layer 312 are exposed atthe bottom of vias 110 and 120. Such etching continues until at least apart of the openings for vias 110 and 120 have reached conductivematerial 208. As such, post etching, metal capping layer 312 is coveringonly a portion of the top-most surface of conductive material 208. Insome embodiments, the etching used to remove the one or more portions ofmetal capping layer 312 comprise a dry etching process, a wet chemicaletching process or a combination thereof. Methods are employed thatselectively etch metal surfaces, such as metal capping layer 312, and donot substantially etch the surrounding dielectric, such as dielectriclayers 204 and 416, and dielectric capping layer 314. A metal etchprocess that is selective to etching metal capping layer 312, and notetching the underlying conductive material 208 is employed. For example,when removing metal capping layer 312 comprising one of Co, Ti, andCoWP, the wet etch process comprises two etchants. A first etchantcomprises a dilute nitric acid solution with typical concentrations of20 to 60 percent volume per volume (% v/v). A second etchant comprises amixture of hydrogen peroxide with typical concentrations of 3 to 15percent weight per weight (% w/w), and a quaternary ammonium compoundwith typical concentrations of 0.2 to 1.5% w/w.

FIG. 4C depicts additional fabrication steps, in accordance with anembodiment of the present invention. In some embodiments, liner material418 is deposited on the exposed portions of dielectric layer 416, suchas the top surface and the sidewalls of vias 110 and 120, the exposedportions of conductive material 208 and liner material 206 at the bottomof vias 110 and 120, the exposed portions of dielectric capping layer314 at the bottom of via 110, and the exposed sidewall portions of metalcapping layer 312 in vias 110 and 120. In some embodiments, linermaterial 418 includes, but is not limited to, Ta, TaN, Ti, TiN, Ru, RuN,RuTa, RuTaN, W, WN, Co, CoW, Mn, MnO, a combination comprising two ormore of the foregoing materials, or any other material that serves as abarrier to prevent a conductive material from diffusing through adielectric material. Combinations of these materials are alsocontemplated to form a multilayered stacked diffusion barrier layer.Liner material 418 is formed utilizing an appropriate depositiontechnique, such as ALD, CVD, PECVD, PVD, sputtering, chemical solutiondeposition, or plating. In some embodiments, the thickness of linermaterial 418 varies depending on the number of material layers withinthe barrier layer, the technique used in forming the same, as well asthe material of the diffusion barrier layer itself. In variousembodiments, liner material 418 is Ta with a typical thickness of about5 nm to about 50 nm.

FIG. 5 depicts additional fabrication steps, in accordance with anembodiment of the present invention. In one embodiment, horizontalportions of liner material 418 are selectively removed from locations510, 520, and 530. Location 510 indicates portions of liner material 418above the top surface of dielectric layer 416 that have been removed.Location 520 indicates portions of liner material 418 above the topsurface of dielectric capping layer 314 and conductive material 208 thathave been removed, thereby exposing portions of dielectric capping layer314 and conductive material 208 at the bottom of via 110. Turning now tothe discussion of the elements seen in both FIGS. 5 and 6, the portionsof liner material 418 that have been removed from location 520 becomethe location where the two bottom portions of via 110 come into contactwith dielectric capping layer 314 and conductive material 208. As such,the bottom portions of via 110 are seen to be in contact with a portionof dielectric capping layer 314 and a top surface of conductive material208 that have been exposed. Therefore, a bottom portion of via 110 islocated over a portion of dielectric capping layer 314, while anotherbottom portion of via 110 is in electrical contact with conductivematerial 208.

Returning now to the discussion of FIG. 5, location 530 includesportions of liner material 418 above the top surface of the exposedportion of conductive material 208 at the bottom of via 120. Theselective removing process includes, but is not limited to, anion-sputtering process with a gas resource including, but not limitedto: Ar, He, Xe, Ne, Kr, Rn, N2 or H2. The ion-sputtering process is theremoval of material by atom bombardment, and works by line of sightallowing the horizontal surfaces to be removed and leaving the verticalsurfaces with minimal sidewall removal. For example, an Ar sputteringprocess is utilized to selectively remove portions of liner material 418using a conventional Ar sputtering process that is used in interconnecttechnology.

In some embodiments, subsequent to the removal of the portions of linermaterial 418, the etching process removes a portion of the exposed metalfrom the surface of conductive material 208, thereby producing a newexposed metal surface at a position below the level of dielectric layer204 and to provide better adhesion of conductive material 622 to thesurface of conductive material 208, as shown in at least FIGS. 6 and 7.Processes for etching the metal, however, should not roughen the metalsurface so much as to create pits or cavities deep enough to retainpockets of moisture during subsequent process operations.

FIG. 6 depicts additional fabrication steps, in accordance with anembodiment of the present invention. In some embodiments, conductivematerial 622 is formed over the sidewalls and bottoms of vias 110 and120, as well as the surface of dielectric layer 416 using CVD, or otherappropriate deposition techniques (discussed above). In someembodiments, conductive material 622 comprises the same or differentconductive material as that of conductive material 208. In someembodiments, conductive material 622 comprises a metal or metal alloyincluding, but not limited to, Cu, Al, W, Ti, Ta, alloys, or any otheruseful conductive material or combinations thereof. Conductive material622, liner material 206, and conductive material 208 are chosen tominimize electrical resistance between them. In one embodiment,conductive material 622 is deposited as plated Cu. In some embodiments,in the case of plated Cu, an initial seed or catalyst layer is depositedprior to plating. The optional seed layer is comprised of a metal ormetal alloy including, but not limited to, Ru, TaRu, TaN, Jr, Rh, Pt,Pd, Co, Cu and alloys thereof. In some embodiments, the deposition isfollowed by a CMP process to remove excess conductive material 622 andliner material 418 above the surface of dielectric layer 416, and toconfine conductive material 622 to vias 110 and 120 formed in dielectriclayer 416.

Additional wiring layers (not shown) are fabricated above interconnectstructure 100 using conventional damascene patterning or subtractiveetch patterning utilizing lithographic, etching and deposition processessuch that no further explanation is required herein for those of skillin the art to understand the invention. One skilled in the art willrecognize that additional cleaning processes may be necessary beforecreating the additional wiring layers. In some embodiments, apassivation layer, a dielectric capping layer, or a protective coating,such as SiN or SiO₂, is deposited (not shown) on surface wires (notshown) to protect the metal surface from environmental conditions. Insome embodiments, a polyimide layer is deposited (not shown) on top ofthe passivation layer with openings for solder connections.

FIG. 7 illustrates a cross-sectional view of a semiconductor devicecontaining a back-end-of-line (BEOL) metal interconnect with a secondliner, in accordance with an embodiment of the present invention.Interconnect structure 700 includes lower interconnect level 202 andupper interconnect level 210 which are separated, in part, by a cappinglayer comprised of metal capping layer 312 and dielectric capping layer314. In some embodiments, lower interconnect level 202 is located abovea semiconductor substrate (not shown) including one or moresemiconductor front-end-of-line (FEOL) devices. Lower interconnect level202 includes dielectric layer 204, and an embedded conductor comprisedof liner material 206, and conductive material 208. Liner material 206acts as a diffusion barrier separating conductive material 208 fromdielectric layer 204. Upper interconnect level 210 includes a seconddielectric layer, i.e., dielectric layer 416, which has two via openingslocated therein for via 110, and via 120. The two via openings for vias110 and 120, each expose a portion of conductive material 208 in lowerinterconnect level 202. The two via openings for vias 110 and 120 arefilled with liner material 418, liner material 824, and conductivematerial 622, which forms an electrical connection between lowerinterconnect level 202 and upper interconnect level 210. Liner material418 acts as a diffusion barrier separating conductive material 622 fromdielectric layer 416. Although the structure shown in FIG. 7 illustratesan interconnect having two vias, in other embodiments, any number ofsuch vias in dielectric layer 416 exist. In such embodiments, certain ofthose vias expose other conductive regions embedded in dielectric layer204.

In accordance with an embodiment of the present invention, interconnectstructure 700 includes a partially landed via, via 110, above conductivematerial 208. Via 110 is partially landed on conductive material 208such that only a portion of the bottom via surface is directly onconductive material 208. A second portion of the bottom via surface ofvia 110 is directly on dielectric capping layer 314. A first portion ofthe sidewall of via 110 is connected to dielectric capping layer 314,and a second portion of the sidewall of via 110 is connected to metalcapping layer 312. In some embodiments, the sidewall of via 110 includesliner material 418. Both metal capping layer 312 and dielectric cappinglayer 314 act as a diffusion barrier separating conductive materials 208and 622 from dielectric layers 204 and 416.

In accordance with an embodiment of the present invention, both vias 110and 120 are constructed with portions of metal liner material 418selectively removed from the bottom of each via. In some embodiments,portions of conductive material 208 directly under the removed portionsof metal liner material 418 are selectively removed. In someembodiments, removal of a portion of conductive material 208 ensuresthat metal liner material 418 is completely removed. In someembodiments, removal of a portion of conductive material 208 texturesthe bottom via surface to aid the adhesion of conductive material 622.Conductive material 622 fills in vias 110 and 120, and directly contactsconductive material 208 to reduce or minimize via resistance. Removal ofportions of metal liner material 418 provides a reduction in overall viaresistance.

In accordance with an alternate embodiment of the present invention,both vias 110 and 120 are constructed with a low resistivity wettinglayer comprised of liner material 824. In various embodiments, linermaterial 824 serves as a wetting agent for reducing voiding duringdeposition of conductive material 622, and has the property of lowresistivity which reduces the overall via resistance of vias 110 and120. The layer comprising liner material 824 visible on the bottomsurface of vias 110 and 120 above conductive material 208 as illustratedin FIG. 7 is a unique structural signature identifying the fabricationmethod used for making interconnect structure 700.

In some embodiments, above upper interconnect level 210 include upperwiring layers (not shown), or escape wiring leading to the surface aboveinterconnect structure 700. In some embodiments, above the upper wiringlayers, there are protective layers (not shown), such as oxides,nitrides, and polyimide films, as are standard in semiconductormanufacture.

FIG. 8 depicts additional fabrication steps, in accordance with anembodiment of the present invention. In some embodiments, subsequent tothe etching of liner material 418 as depicted and described in furtherdetail with respect to FIG. 5, liner material 824 is deposited on theexposed portions of the top surface of dielectric layer 416, the exposedportions of conductive material 208 at the bottom of vias 110 and 120,the exposed portion of liner material 206 at the bottom of via 110, theexposed portions of dielectric capping layer 314 at the bottom of via110, and the exposed sidewall portions of liner material 418 in vias 110and 120. In some embodiments, liner material 824 includes, but is notlimited to, Cu, Ru, Co, or a combination comprising two or more of theforegoing materials, or any other material that serves as a wettingagent for reducing voiding during deposition of conductive material 622(shown and described in at least FIGS. 6 and 7), and has the property oflow resistivity, typically less than 100 micro-ohm centimeters. Linermaterial 824 is formed utilizing an appropriate deposition technique,such as ALD, CVD, PECVD, or PVD. In various embodiments, liner material824 is Co with a typical thickness of about 5 nm to about 50 nm. Thelayer comprising liner material 824 visible on the bottom surface ofvias 110 and 120 above conductive material 208 as illustrated in FIG. 8is a unique structural signature identifying the fabrication method usedfor making interconnect structure 700.

Having described embodiments for a metal interconnect comprised of a viawith reduced resistance and methods of fabrication removing the metalliner at the bottom of the via (which are intended to be illustrativeand not limiting), it is noted that modifications and variations may bemade by persons skilled in the art in light of the above teachings. Itis, therefore, to be understood that changes may be made in theparticular embodiments disclosed which are within the scope of theinvention as outlined by the appended claims.

In certain embodiments, the method as described above is used in thefabrication of integrated circuit chips. The fabrication steps describedabove may be included on a semiconductor substrate consisting of manydevices and one or more wiring levels to form an integrated circuitchip.

The resulting integrated circuit chip(s) can be distributed by thefabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

What is claimed:
 1. A method of fabricating a semiconductor interconnectstructure, the method comprising: providing a semiconductor structureincluding a first dielectric layer having a first electricallyconductive structure embedded therein, a second dielectric layer locatedabove the first dielectric layer, the second dielectric layer and thefirst dielectric layer having a segment of a dielectric capping layerlocated therebetween that is (i) non-overlapping with and (ii) in planewith a segment of a metal capping layer located therebetween, thesegment of metal capping layer covering at least a portion of a topsurface of the first electrically conductive structure; forming anopening in the second dielectric layer and the metal capping layer,thereby exposing at least a portion of the first electrically conductivestructure and a portion of the dielectric capping layer; and forming asecond electrically conductive structure in the opening, such that afirst bottom portion of the second electrically conductive structure islocated over a portion of the dielectric capping layer that abuts thefirst dielectric layer, and such that a second bottom portion of thesecond electrically conductive structure is in electrical contact withthe portion of the first electrically conductive structure.
 2. Themethod of claim 1, wherein forming the second electrically conductivestructure in the opening further comprises: depositing a first linermaterial in the opening such that the first liner material is over aportion of the first electrically conductive structure; removing aportion of the first liner material that is over the portion of thefirst electrically conductive structure; and filling the opening with asecond conductive material, such that an electrically conductiveconnection with low resistivity is formed between the first electricallyconductive structure and the second electrically conductive structure,wherein low resistivity is defined as resistivity less than 100micro-ohm centimeters.
 3. The method of claim 2, further comprising:depositing a second liner material in the opening, thereby covering aportion of at least one of the first liner material, the dielectriccapping layer, and the first electrically conductive structure, whereinthe second liner material is selected for low resistivity and forwettability of the second conductive layer.
 4. The method of claim 3,wherein the second liner material comprises at least one layercomprising one or more of: Cu, Ru, and Co.
 5. The method of claim 2,wherein removing the portion of the first liner material comprises:removing the portion of the first liner material utilizing a linermaterial removal process that is selective to removing one or morehorizontal portions of the first liner material with minimal removal ofone or more vertical portions of the first liner material.
 6. The methodof claim 5, wherein the liner material removal process comprises: anion-sputtering process with a gas resource including at least one of:Ar, He, Xe, Ne, Kr, Rn, N2 and H2.
 7. The method of claim 1, wherein thedielectric capping layer comprises a dielectric material that inhibitsmetal diffusion between the second electrically conductive structure andthe first dielectric layer.
 8. The method of claim 1, wherein the metalcapping layer comprises at least one layer comprising one or more of:Co, Ru, W, Ta, Ti, P, and Rh.
 9. The method of claim 1, wherein formingthe opening in the second dielectric layer and the metal capping layercomprises: forming the opening in the metal capping layer using a metaletch process that is selective to etching the metal capping layer whileminimizing removal of the first conductive material and the dielectriccapping layer.
 10. The method of claim 9, wherein the metal etch processcomprises: a first etchant comprising a dilute nitric acid solution withconcentrations of 20 to 60 percent volume per volume (% v/v); and asecond etchant comprising a mixture of hydrogen peroxide withconcentrations of 3 to 15 percent weight per weight (% w/w), and aquaternary ammonium compound with concentrations of 0.2 to 1.5% w/w.